Sublimation apparatus



Feb' 2' 1943' F. J. HANsGlRG 2,309,644

SUBLIMATION APPARATUS Filed April 9. 1941 2 Sheets-Sheet 2 Patented Feb. 2, 1943 SUBLIMATION APPARATUS Fritz J. Hansgrg, San Mateo, Calif., assignor, by mesne assignments, to The Anglo California National Bank of San Francisco, San Francisco, Calif., a national banking association, as

trustee Application April 9, 1941, Serial No. 387,643 In Japan December 24, 1938 7 Claims.

This invention relates to the refining of sublimable materials, and more particularly to the recovery and rening of magnesium, especially in the form of impure dust, by sublimation. l

The word sublimation as used herein has its usualscientific connotation, to wit, the conversion of solid material to the vapor state and condensation of th`e vapor to the vsolid state without formation of the liquid state. In the practice of sublimation processes, therefore, the

material to be rened is heated under a pressure such as to produce vapor directly from the solid phase, the sublimed vapor being then condensed direcuy to the solid phase.

It has been proposed to reiine impure compact magnesium metal produced by electrolysis or recovered from scrap metal, by sublimation. However, sublimation of magnesium is too slow for practical purposes except at Very low pressure. This is attended with the drawback that the rush of vapor from the retort to the condenser entrains a substantial amount of non-volatile impurities heavily contaminating the resulting condensate. Particularly, this inconvenience occurs in the course of the reduction of magnesium oxide with the aid of carbon according to my Patent No. 1,884,993, granted October 25, 1932, in the first stage of which, on shock-chilling the mixture of magnesium vapor and carbon monoxide disengaged, there is obtained a dusty condensate in an extremely fine division, from which metallic magnesium has to be recovered, in a second stage of operation, by distillation or sublimation. 'I'his intermediate product includes not onlyimpurities coming from the ore started with, but-owing to partial reversion of the reduction reaction MgO-i-C-Mg-l-CO being by no means completely avoidablealso considerable amounts of magnesium oxide and carbon. If in this second stage it is attempted to refine the extremely iinely divided dusty condensate of the first stage by a sublimation operation in which commercially economical rates of vapor flow are obtained, the vapor evolved will carry over not only non-sublimable impurities but also virgin magnesium dust in itself, even when the dusty intermediate product was made into compacted bodies before further treatment. As' a consequence thereof, there will not be recovered metal answering as to purity thepractical rev quirements.

It is among the objects of this invention to provide a sublimation apparatus in which commercially economical rates of sublimation are attained while producing refined material of improved purity as compared with products produced according to previously proposed sublimation methods.

Yet another object is to provide apparatus for sublimation in which the speed of vapor flow is controlled to prevent, or substantially prevent, the carrying over of any impurities from the retort into the condensed product.

A special object is to provide apparatus for economically recovering magnesium metal from dust produced by carbo-thermic methods, which apparatus produces massive magnesium of exceptionallyhigh purity.

Still another object is to provide an apparatus for performing sublimation operations which embodies means for controlling the speed of flow of the vapor from the retort to the condenser.

A further object is to provide apparatus of the foregoing type which is adapted to high vacuum operation and in which the retort is substantially free from stresses which would normally result from the evacuation cf the retort.

Other objects will appear from the following description.

'I'he invention may be described with reference to the accompanying drawings in which Fig. 1 is a vertical section through the preferred embodiment of an apparatus in accordance with the invention; and Fig. 2 a horizontal section illustrating constructional details and taken on the line lI-II, Fig. 1; and Fig. 3 is a longitudinal vertical section through a retort representing an alternative embodiment ofthe invention.

In accordance with the invention, magnesium dust or other sublimable material is refined by heating it to a temperature and under a pressure such as to cause the material to sublime, and passing the vapor to a condenser and condensing the vapor, while restricting the speed of vapor travel on the way to the condenser in such manner that the vapor does not carry any substantial amount of impurities, and most suitably while operating, forpurposes of economy,

as nearly as practicable to the maximum rate at` which said impurity entrainment is avoided.

The essential elements of the sublimation apparatus provided by the invention include a retort member for vaporizing sublimable material charged therein and a condenser member for condensing, as a solid deposit, the vapor evolved, in combination with means adapted to reduce the speed of the vapor ow on the path from the retort to the condensenby causing the vapor released i'rom the charge to escape, through a plurality of relatively small passageways, into a central relatively large unobstructed channel, longitudinally extending along substantially the full depth of the charge and opening into the condenser. According to a preferred embodiment of the invention the apparatus comprises a longitudinally extended receptacle of substantial tubular shape, closed at the bottom of the lower portion which is adapted to be heated, to serve as the retort, and provided with a removable cover at the top of the upper portion which is adapted to be kept cool to serve as the condenser, and equipped with means for reducing the absolute pressure within the receptacle, in combination with a flow-regulating device forming a central duct member with lateral inlet openings for permitting the entry of the vapor released from the charge into the interior duct along its lengths, the said duct member by displacement reducing the radial extent or the charge and providing a relatively large, free passageway for the vapors rising toward the condenser.

Apparatus embodying the invention and particularly suited to the practice of the method described is shown in Figs. l and 2. The apparatus comprises an outer pressure-tight metallic shell I within which there is disposed a pressure-tight cylindrical metallic container 2 the lower portion R oi which acts as a retort chamber and upper portion C of which provides a condensing chamber. To conserve heat shell I is provided with insulation, suitably a lining 3 constructed from insulating brick, the inner face of lining 3 being spaced from container 2 in such manner as to provide an annular space t between the container and the lining Means are provided within space S for supplying heat to a charge of material disposed Within the retort P.. In the embodiment shown, this is accomplished by a coiled electrical resistor 5 connected by wires 6 and 60. to a source of electric current, not shown, whereby heat for sublimation is supplied by radiation to the retort portion of container 2. Pyrometers may be arranged at suitable points for measuring and controlling the temperature.

Disposed within the condensing chamber C of container 2 is a removable metallic liner member 8 which is supported, for example, by angles 9 fastened to the container wall to hold the liner in proper position within the condensing chamber. Desirably this mounting is such as to prevent entry of sublimed vapor between the liner and the container. Usually, it will be desirable to provide means for abstracting heat from the condensing chamber to facilitate or control the condensation of vapor on liner 8. In the embodiment shown this may be accomplished by circulating a cooling fluid, such as air, through a coil I0 of pipe surrounding the condensing chamber within the annular space Container 2 is provided with a suitable cover I I which may be secured in pressure-tight manner by any suitable means such as nuts I2 cooperating with bolts I3. Adjacent its top the container 2 is provided with an outwardly extending flange I 00 welded or otherwise connected to the container so that the joint therebetween is pressure-tight. For handling the container hooks |04 may be connected to cover i I. When the container is inserted into the apparatus the fiange |00 engages a flange I0l similarly connected to the upper end of shell I, as shown in Fig. 1. This serves to suspend the container properly in the -between each pair of the successive members,

the lowermost of which is disposed near the bottom of container 2, the uppermost member 22 being surmounted by a conical cap 23 with slots 23a or other foramina. As is to be seen from the drawings, the flow-regulating device preferably occupies a substantial part of thi;l diameter of the retort, so that the charge surrounds this device in the shape of a relatively thin annular layer and is thus adapted to be uniformly heated from the outside .and to give off the vapor rapidly through its full depth.

For charging the apparatus, cover II is provided with an opening of appropriate size which may likewise be closed to maintain any desired vacuum within the container, As shown, the cover is provided with an opening having an extension I4 provided with a closure member I." removably held in place by bolts I6 and nuts Il this connection being likewise pressure-tight. Liner 8 carries a tubular charging shaft I8 so positioned as to receive material introduced through opening I4 and direct it downwardly into thi' retort chamber R, this being further assisted by a funnel-like member I9 carried by the bottorn of liner S. The liner may be of the split type for ease in removing and recovering the condensate, which will build up on the wall of the linear generally as indicated by the broken lines in Fig. l. The liner may be provided with any suitable means for lifting it from and re turning it to the container 2. In the embodiment shown this is accomplished by web members 20 connected to the upper end of the liner and provided with openings 2| for receiving lifting hooks. These webs serve also to support the charging shaft I8. ,i

In the use of this apparatus for: practicing the method provided by the invention, liner 8 is placed in the retort and cover II is connect ed in pressure-tight manner by nuts I2 and bolts I3. The assembly is then placed in the furnace and nuts |03 are screwed onto nuts |02 to make a pressure-tight connection between flanges |00 and |0I. A charge of material to be rened, impure magnesium, for instance, is introduced into the apparatus after removing closure I5 by dumping the material into opening I4 whereby it will be discharged into the retort chamber. Closure I5 and cover II are then made pressure-tight, heat for causing sublimation is supplied by passing electric current to resistor 5, and container 2 is evacuated to the necessary extent. This may be done by connecting the container to a vacuum pump through a pipe 24, provided with a valve 24a, which passes through closure I5 or by effecting reaction between a portion of the magnesium and a gas reactive therewith such, for example, as air, nitrogen, carbon monoxide, chlorine, or the like, as disclosed and claimed in my copending application Serial No. 355,087, filed August 2l, 1940, now Patent No. 2,240,817.

The container I is evacuated by a vacuum pump connected to a conduit 28 which opens into space 4, to produce the same vacuum as is produced within container 2. As a consequence the walls of the latter will not be subjected to stresses caused by pressure differential, so that this container may be of lighter and less expensive construction than has been necessary heretofore.

Increasing the rate of heat transfer to the interior of the charge may be accomplished by providing a series of spaced, radially positioned radiating plates or fins 25 connected to the container wall which preferably extend the full length of the retort. Moreover the members 22 may be rigidly connected with longitudinally running fins 26, for instance welded thereto, with the view of enabling the flow-regulating means to be easily lifted, as unitary structure, from the container by means of eyed hooks 21 or the like, and these plates or fins may also serve as radially extended radiating elements which are preferably disposed, as appears from Fig. 2, alternating with the plates or fins 25.

.desired for any reason, a binder, preferably of inert and protective nature, may be used in compacting the dust.

'I'he maximum permissible speed of vapor travel will depend on the temperature and pressure conditions and consequently on the material to be sublimed, moreover, on the particu-'- lar construction of the now-regulator used. To illustrate the mutual relations of these different conditions, exact data may be given in regard to the refining of magnesium dust of the kind repeatedly referred to above. To obtain a condensate of the highest purity from this special material, the speed of vapor flow should not exceed about 4.5 meters per second. With the charge heated to a temperature oi' '750 C. (at which temperature the compacted dust will still `be solid due to its peculiar characteristics) and container 2 operated at 1 mm. pressure, and with heat supplied at a rate such as-to vaporize 4 grams of magnesium per second, there will be formed and transferred to the condenser,11,200 liters of vapor per second. The maximum rate of vapor travel of 4.5 meters per second will be effected by now-restricting means as illustrated providing a total open base area of conical members 22 amounting to 2.5 square meters. This area would be supplied by ten cones 22 arranged as shown and each having a base diameter of 900 mm. and a diameter of 700 mm. at its upper truncated end.

Although the invention has been described as applied particularly i J the refining of magnesium dust of the type referred to, it will be understood that the principle of the method and the apparatus are applicable to refining magnesium in other forms and to refining other sublimable materials of both metallic and non-metallic nature.

Various modifications of the apparatus and permissible. For instance, although liner 8 may be of a metal such as iron or steel, it may advantageously be made from the material being sublimed, e. g., in the case of magnesium a rolled sheet of pure magnesium. Such a liner with its deposit of condensed `material may then be removed and used directly. thus avoiding the special construction needed for or difficulties that' may be encountered in removing the de posit from a ferrous metal liner.

Another possibility is shown in Fig. 3. As

, shown. the upper, or condensing, end of container 2a is made of inverted conical form, and chains are suspended from cover I Ia so that their lower ends lie close to the wall, as shown. By providing the wall of the conical condensing chamber with a coating of graphite or other material which acts to prevent the adherence of condensed magnesium thereto, the body of condensed metal will embed the chains 30 and may be lifted out as a unit upon removal of the cover Ila.

'Ihis application is a continuation in part of my copending application filed February 26, 1941, Serial No. 380,589.

According to the provisions of the patent statutes, I have explained the: principle and method procedure shown and described are, of course,

of operation of my invention and have illus' trated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. Sublimation apparatus comprising a pressure-tight outer shell, a' pressure-tight container arranged within said shell and spaced therefrom to form an annular space therebetween, the lower portion of said containerI forming a' sublimation retort member and the upper portion a condensing chamber member, vmeans for heating said retort to make sublime sublimable contents of a charge of material contained therein, a condensing surface removably disposed in said chamber for condensation of sublimed material thereon, means for cooling vsaid surface and condensing sublimed vapor thereon, means disposed in said retort adapted to provide a predetermined rate of vapor fiow from the retort to the condenser chamber, and means for evacuating said container and said annular space to relieve stress on the outside of said container walls due to evacuating said container.

2. Sublimation apparatus comprising anl outer pressure-tight shell, a pressure-tight container arranged within said shell and spaced therefrom to form an annular space therebetween, the

lower portion of said container forming a sublimation retort member and the upper portion a condensing chamber member, means disposed in said space for heating said retort to sublime a charge of material contained therein, a liner removably disposed in, said condensing chamber for condensation of subiimed material thereon, means disposed in said space for cooling said liner and condensing sublimed vapor thereon, means associated with said outer shell for evacuating said space to relieve stress on said container walls due to evacuating said container, means for evacuating said container, and vapor flow controlling means disposed in said retort comprising a plurality of truncated conical members constructed and arranged to cause the vapor generated in the retort to enter their bases and iiow upwardly into the condenser, the area of said bases providing a predetermined speed of vapor iiow and said cone assembly being connected to a plurality of spaced metallic ns extending radially of the retort chamber, and a plurality of fins connected to said container wall within said retort chamber and extending radially of the retort between said first-named ns.

3. Apparatus for sublimation comprising a retort member for vaporizing sublimable material charged thereir. and a condenser member for condensing, as a solid deposit, the vapor evolved, in combination with means adapted to reduce the speed of the vapor released from the charge and. passing from the retort to the condenser,

by causing the vapor to escape through a plurality of relatively small passageways into a centrai relatively large unobstructed channel longitudinally extending along substantially the full depth of the charge and opening into the condenser.

Apparatus for sublimation equipped with means for reducing the absolute pressure therewithin, comprising a retort member for Vaporizing sublima-ble material charged therein and a condenser member for condensing, as a solid deposit, the vapor evolved, in combination with means adapted to reduce the speed of the vapor released from the charge and passing from the retort to the condenser, by causing the vapor to escape through a plurality of relatively small passageways into a central relatively large unobstructed channel longitudinally extending along substantially the full depth of the charge and opening into the condenser.

5. Apparatus for sublimation comprising a longitudinally extended receptacle of substantial tubular shape, closed at the bottom of the lower portion which is adapted to be heated, to serve as a retort, and provided with a removable cover at the top of the upper portion which is adapted to be kept cool, to serve as a condenser, and equipped with means for reducing the absolute pressure within the receptacle. in combination with a central-duct member with relatively small lateral inlet openings along its length. permitting the entry of the vapor released from the charge into a relatively large interior duct for the vapor rising toward the condenser, the said duct member being adapted to reduce, by displacement, the radial extent of the charge.

6. Sublimation apparatus comprising a pressure-tight outer shell, a pressure-tight container arranged within said shell and spaced therefrom to form an annular space therebetween, the lower portion of said container forming a sublimation retort member and the upper portion a condensing member, means disposed in said space for heating said retort to sublime the subllmable contents of a charge of material contained therein, a liner removably disposed in said chamber for condensation of sublimed material thereon, means disposed in said space for cooling said liner and condensing sublimed vapor thereon, means disposed in said retort for controlling speed of travel of sublimed vapor from the retort to the condenser chamber, said ow-controlling means comprising a plurality of super imposed truncated conical members constructed and arranged so that vapor generated in the retort enters their bases and is directed into said condensing chamber, the open area of said bases being such as to provide a predetermined rate of vapor ow from the retort to the condensing chamber, means for evacuating said container, and means associated with said outer shell for evacuating said space to relieve stress on the outside of said container walls due to evacuating said container.

'2. Apparatus for sublimation comprising a retort member, a condenser member, and a removable liner in said condenser for condensing thereon the material to be sublimed and formed from said material, said liner being a sheet or plate of pure magnesium.

FRITZ J. HANSGIRG. 

